The present invention relates to blow-molded containers of biaxially oriented thermoplastic materials, typically polyethylene terephthalate, that are especially adapted to be filled with a hot liquid or semi-liquid product and hermetically sealed, and which are generally referred to as thin-walled hot-fill containers. The invention particularly relates to improvements in container design to achieve a filled container that, when cooled, retains a desired container configuration despite the development of a partial vacuum within the container, and provides enhanced support of any label applied to the container even when subjected to sidewall impact.
Thin-wall hot-fill containers are typically used for packaging of liquids which must be placed in the container while hot for aseptic packaging. During the filling process, the container is subjected to elevated temperatures and may be subjected to some small positive internal pressures. The container is immediately capped so that no appreciable cooling or contamination of the container contents occurs prior to the hermitic sealing. As the product subsequently cools, a negative internal pressure is formed in the sealed container. Any flexible wall of the container will elastically deform inward to the extent necessary to at least partially reduce the negative pressure within the container. Thin-wall hot-fill containers of the prior art typically include a plurality of vacuum panels specially designed to elastically deform in a controlled manner, thus preventing any large uncontrolled shape distortion. The vacuum panels are typically arranged around the circumference of a middle portion of the container and are typically covered by a wrap-around label held within the margins of an area commonly identified as the label panel.
Many styles and geometric patterns have been developed for the vacuum panels. The variations are all intended to address various concerns about the container performance and shape retention when dropped, when vertically stacked, when pinched by manually gripping the container, etc. To address these concerns the vacuum panels often include raised central wall portions, post areas between the vacuum panels, circumferential land areas above and below the vacuum panels, longitudinal and circumferential recessed ribs, hinge portions, etc. As the wall thickness of the containers is reduced from the already thin dimension of typically less than ½ mm, the various problems associated with thin-wall hot-fill containers become exacerbated. A particularly difficult problem is presented by side impacts that tend to permanently deform the sidewall of the container. A more general problem is the competing desires of providing sufficient stiffness in specific areas of the label panel, while still permitting other areas to yield in the intended manner for successful hot-fill performance. A common problem arises in the area of and outside each corner of the vacuum panels, where creases can develop that can contribute to large scale deformation of the container side wall.
What is needed is a thin-wall hot-fill container that provides a large range of flexibility while retaining sufficient support of any label applied to the container even when subjected to sidewall impact. What is particularly needed is a thin-wall hot-fill container that provides for enhanced resistance to container deformation is the area of the vacuum panel corners.